Classification of newborns according to birthweight and gestational age is a useful clinical and epidemiologic tool to identify newborn infants at high risk for excess morbidity and mortality. In developing countries birthweight and gestational age cannot be measured directly. Moreover, preterm and low birth weight lose up to 10% of their birthweight during the first week. Using the statistical technique of recursive partitioning we recently demonstrated that head and chest circumference measurements accurately identified preterm, low birthweight newborns on data from Ethiopia. The rationale for employing other body measurements as surrogate for birthweight is dependent on their stability during the first week. We are currently examining the results of serial measurements of head, chest, midarm circumference, body weight and length measurements in a cohort of 600 Ethiopian newborns in order to determine their pattern during the first week.